Why Are Some Ancient Bodies Perfectly Preserved? Chemistry of a Peat Bog
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Bodies recovered from peat bogs retain skin, hair, clothing and stomach contents after two thousand years, which no ordinary burial preserves. The conditions that achieve that also destroy the bones.
Why they survive
Decay requires oxygen, warmth and microorganisms, and a peat bog denies all three. Waterlogging excludes oxygen almost completely below the surface. Temperatures are low. The water is strongly acidic, which suppresses the bacteria that would otherwise consume tissue. And the moss that forms peat releases compounds that bind nitrogen and effectively tan the skin, chemically similar to the tanning of leather, which preserves it as a tough dark material. The combination stops decay almost entirely for soft tissue. The same acidity dissolves calcium, so bones and teeth are demineralised and frequently reduced to nothing, which is why these bodies are flexible and why skeletal analysis is usually impossible on them.
What survives and what is learned
The preservation supplies evidence no other burial context does:
- •Skin, including fingerprints and tattoo-like markings in some cases
- •Hair, including cut and styled arrangements
- •Clothing, leather goods and cordage, which decay everywhere else
- •Stomach and intestinal contents, giving the last meal in detail
- •Facial features sufficient for reconstruction
- •Evidence of injury, which is how the manner of death is established
How they died
A substantial number show violent death, and the pattern has produced a long argument. Several well-known bodies bear injuries indicating that they were killed rather than dying naturally, with cut throats, blows to the head, strangulation and in some cases several of those together, which is frequently described as excessive and taken as evidence of ritual. Interpretations proposed include sacrifice, execution of criminals, punishment of people accused of particular offences, and killing of prisoners. The evidence rarely distinguishes between them, and Roman writers describing northern European practice are late, hostile and not reliable witnesses. What can be said is that a proportion of these people were killed and placed in bogs deliberately, which is not how most people in those societies were treated.
What the last meal shows
Stomach and gut contents are among the most informative things these bodies supply and the analysis is detailed. Identifying seeds, grains, pollen and plant fragments establishes what was eaten and, from what was in season, the time of year of death. Several bodies show a final meal of a gruel containing many species including weeds of cultivation, which has been read as indicating either an ordinary poor diet or a ritual preparation, depending on the researcher. The absence of summer fruits in some cases points to winter or spring death. Chemical analysis of hair records diet over months before death and has shown changes in the final weeks in at least one case. Parasite eggs in the gut indicate health and living conditions directly.
The problem with the collection
The bodies known are a biased and diminishing sample. Most were found during peat cutting, so they come from areas where peat was worked commercially, and the great majority were found before archaeological techniques existed, with many destroyed, reburied or lost and only the most striking retained. Machine cutting from the twentieth century destroys anything it encounters and finds are correspondingly rarer. Drainage of bogs for agriculture and for fuel has destroyed the conditions across enormous areas, and a body in a drying bog decays rapidly once oxygen reaches it. Climate change is accelerating that. Conservation of recovered bodies is itself difficult, since removing one from the conditions that preserved it starts the decay the bog had stopped.
The takeaway
Waterlogging, cold, acidity and compounds released by peat moss together stop decay and tan the skin, while the same acidity dissolves the bones. The preservation supplies clothing, hair, facial features and the contents of the stomach. Several bodies show violent death by multiple means, which is read as ritual, as execution or as punishment, and the evidence rarely distinguishes them.